PSI - Issue 84

Marco Civera et al. / Procedia Structural Integrity 84 (2026) 49–56

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(a)

(b)

Fig. 3. (a) Possible geometry of scour holes around the pier foundations. Dashed lines represent clearly visible excavation edges, while dotted lines indicate some potential edges (uncertain and not clearly visible). (b) Top-down view of pier P2, as seen from the North-East side.

2.2. 1998 and 2009-2011 Structural Interventions The previous description represents the initial structural configuration of the Amedeo VIII bridge. After that, the 1998 works included conservative rehabilitation of R.C. structures ( risanamento conservativo ), replacement of transverse and longitudinal expansion joints, protection of piers and abutments with newly added stone blocks, and additional interventions on non-structural elements such as sidewalks and waterproofing. After these interventions, the 2000 campaign, following core drilling and compressive tests on cubic specimens, returned R ck ≅ 20 N/mm 2 . The reinforcement steel rebars were tested as well, finding a tensile strength of circa 435 N/mm 2 . Dynamic testing was also carried out on the bridge as part of the same investigation campaign to evaluate the dynamic response of one deck under excitation (Table 1).

Table 1. Modal parameters as identified in the Geotek report (Formento, 2000) before retrofitting. mode natural frequency [Hz] damping ratio [-]

mode natural frequency [Hz] damping ratio [-]

#1 #2 #3

4.0 5.6 6.2

0.11 0.08

#4 #5

10.5 11.5

0.05 0.04

0.07 Unfortunately, the available documents do not include any other detail concerning the structure's vibrational behaviour, such as the corresponding mode shapes or the locations of the accelerometers (not even the investigated spans). In any case, these cannot be directly compared to current measures, as they were performed before the retrofit. Nevertheless, they provide some insight into the expected range of frequencies of interest. Regarding the retrofitting strategy, this was intended to preserve the original Gerber hinge static system, pairing it with external post-tensioning with longitudinal tendons (external to main beams but inside the deck), anchored transversely by new R.C. anchorage beams and deviated through new R.C. diaphragms (refer to Fig. 2.e for the exact configuration). These external tendons are made of 12- or 4-strand cables (0.6” strands, with f ptk = 1800 N/mm 2 ), with design tensile stresses spi ≈ 1360 N/mm 2 ; also, additional mono-strand tendons and pre-stressing DYWIDAG bars (Ø26 and Ø36 mm) were used in diaphragms and anchorage areas. Importantly, these external cables represent a critical point of the current structure, worth being monitored. Unfortunately, economic limitations did not allow for the deployment of specific sensors on the prestressing cables. However, Fibre Bragg Grating (FBG) sensors were installed directly on the prestressing cables to measure stresses and verify force transfer during one day (April 20, 2011) of static tests. The results (summarised in Fig. 4) confirmed that the prestress forces were effectively introduced and distributed as designed, ensuring that the new tendons were carrying the intended load share. The retrofitting also included some complementary works, such as the complete replacement of expansion bearings (fixed and movable), ensuring proper longitudinal sliding and seismic response; the demolition and reconstruction of